1. Field of the Invention
The present invention relates generally to an armature structure of a radial gap type electric rotary machine. More particularly, the invention relates to an armature structure of a radial gap type electric rotary machine, in which respective salient poles of armature are positioned by one of two rings and reluctance is lowered by the other ring.
2. Description of the Related Art
In a conventional electric rotary machine, in which an armature is constituted by a plurality of ring-shaped plate yokes made of a soft magnetic plate member such as silicon steel plate or the like and stacked in an axial direction, each ring-shaped plate yoke having a plurality of salient poles radially formed, since the ring-shaped plate yoke is punched out integrally with a plurality of salient poles, the salient poles are not structurally separated and therefore a resultant armature will have superior magnetic efficiency (low reluctance). However, since usually a winding is wound directly on each salient pole, winding operation is troublesome. Particularly, in case of an inner rotor type electric rotary machine, winding operation is quite difficult. As a result, the winding operation will require a longer time and a space factor of the winding cannot be increased. Furthermore, because the winding is done by flyer winding, tensional stress may be applied to a wire during the winding operation to restrict insulation reliability of the winding portion.
However, in recent years, a rare earth magnet having high energy product has been developed and structure of the electric rotary machine has been reviewed by analysis of magnetic circuits using a computer. This results in findings that a divided armature type electric rotary machine, in which improvement in efficiency in the winding operation and increase in space factor are expected while reluctance is slightly increased, can achieve higher performance and low cost. Therefore, there is a growing demand for division of an armature.
As an example of the divided type armature, a conventional type armature yoke which is constituted by a plurality of ring-shaped plate yokes stacked in their axial direction is divided into salient pole portions and a winding is provided on each of the separated salient pole portions, then the separated salient pole portions are joined at divided places by laser or the like (welding or the like) to be reinstated into an armature. This method needs much labor because the conventional armature is once divided and then joined again. Moreover, the separated salient pole portions have to be put back together while maintaining the stacked condition appropriate, so it is necessary to set the separated salient pole portions in a die, tooling or the like which ensures assembling precision satisfactorily and to securely weld them on a one-by-one basis. Therefore, high precision is required and workability is low. Furthermore, mechanical and magnetic characteristics are significantly degraded at the joined (welded) portions inherently. Thus, the conventional divided type armature still has a few problems to be solved.
In order to solve such defects involved in the divided type armature as set forth above, the inventors have proposed methods to divide an armature into a structure completely different from the conventional structure in Japanese Unexamined Patent Publication No. Heisei 11-355981 and Japanese Unexamined Patent Publication No. 2000-4566. These methods apply an invention in the armature structure, which is adapted to satisfactorily turn features of the divided type to advantage for the winding operation and joining the salient poles. However, a hole for positioning and joining the salient poles is required on a stator ring (which refers to xe2x80x9couter casing of the electric rotary machinexe2x80x9d) which functions as a magnetic circuit as well. The hole presents discontinuity in the magnetic circuit to cause outward emission of leakage flux, which is disadvantageous in view of electromagnetic compatibility (EMC), etc. to which importance is attached recently. Another problem resides in lowering of electromagnetic conversion efficiency, which is caused by increase in reluctance in the ring itself and salient pole joining portions. And still another problem resides in degrading external appearance of a product because the lower ends of the salient poles are exposed through the hole or groove of the stator ring.
It is an object of the present invention to provide a rotary gap type electric rotary machine with a divided armature comprising a plurality of separated salient poles and a ring which magnetically and mechanically couples the salient poles, wherein a stator ring is provided with no hole for positioning and fixing separated salient poles whereby leakage flux resulting from magnetic discontinuity can be reduced and at the same time electromagnetic conversion efficiency of an electric rotary machine can be enhanced.
Another object of the invention is to improve the external appearance and decency of an electric rotary machine by preventing the lower ends of the salient poles from being exposed through the outer surface of the electric rotary machine.
According to one aspect of the invention, there is provided a radial gap type electric rotary machine comprising a field magnetic pole consisting of a permanent magnet which is rotatably supported and an armature assembly having a plurality of separated salient poles opposing the field magnetic pole with a small air gap therebetween and radially arranged with respect to a rotation axis of the electric rotary machine, wherein the armature assembly includes a first ring made of a soft magnetic member for receiving a plurality of salient poles and a second ring made of a soft magnetic member for receiving the first ring.
The first ring has substantially rectangular slits or holes for guiding and fixedly holding the salient poles and the slit or the hole extends in parallel to the rotation axis.
Each salient pole of the armature assembly may be formed by stacking a plurality of soft magnetic plates in a circumferential direction.
The first and second rings may be fixedly bonded together.
One of the first and second rings may be made of a flat metal plate and formed into a ring configuration, and the salient pole is not positioned at a joint between a first rolling end and a second rolling end of the ring.
Both the first and second rings may be made of a metallic flat plate and formed into a ring configuration, and an angle formed by the joint between the first rolling end and the second rolling end of the ring may be set to have an offset in a range of from 30xc2x0 to 330xc2x0 inclusive in terms of a center angle.
The second ring may have a wall thickness equal to or greater than a wall thickness of the first ring, and the second ring may have an axial length equal to or greater than an axial length of the first ring.
Substantially disc shaped flanges having bearing mechanism at the center portions thereof may be fixed by welding on both axial end surfaces of second ring.
At least one of the first and second rings may be formed of vibration damping steel sheet which is made by integrating a synthetic resin made of a high polymeric material with a metal and has a damping effect.
The electric rotary machine may be a brushless DC motor.